HYDROLYSIS OF CATIONS - FORMATION-CONSTANTS AND STANDARD FREE-ENERGIES OF FORMATION OF HYDROXY COMPLEXES
HYDROLYSIS OF CATIONS - FORMATION-CONSTANTS AND STANDARD FREE-ENERGIES OF FORMATION OF HYDROXY COMPLEXES
复制标题
DOI：
10.1021/ic00158a016
复制
发表时间：
1983-01-01
影响因子：
4.6
通讯作者：
BARNUM, DW
中科院分区：
文献类型：
--
作者：
BARNUM, DW
本文研究了元素周期表中金属离子的单核和多核羟基配合物的形成常数和标准自由能。一些经验的相关性，使人们有可能预测这些常数的粗略值。对于单核络合物，方程为AGf 0（M（OH），，|= AGf {M| + By+ Cyl+ D/y，其中B、C和D是经验参数，y是配位氢氧根离子的数目。这些参数受到限制可接受值的约束。例如，B、C和电负性相互关联。这个方程可以重新排列，定义一个新的函数，U，它与y成线性关系。这允许未测量的自由能的插值，因此形成常数。对于单核复合物，log Kly的预测值具有约±0.5的不确定性。对于多核羟基配合物，Baes和Mesmer提出的一个关系式作了一些修改，并用于预测未知的生成常数，其不确定度（log Kxy）约为±0.5 y。汞（II）和银（I）形成特别稳定的“线性”络合物，但由于从M（OH）2到M（OH）3物种发生结构变化，因此不遵循上述相关性。与八面体配位的二价金属水离子相比，四面体配位的Be 2+（aq）离子比预期的酸性更强。每个氢必须比八面体复合物中携带更大部分的正电荷，这使得质子的去除更容易。含水Sn 2+也是异常酸性的，并且建议它在主配位球中的水分子也比对于“正常”八面体配位的金属离子所期望的少。以前的研究人员在确定某些金属离子如铋（III），铈（IV），锆（IV）的多核羟基配合物的形成常数时遇到的实验困难的一个原因。
The formation constants and standard free energies of formation of both mononuclearand polynuclear hydroxy complexes of metal ions throughout the periodic table have been examined. Some empirical correlations are presented that make it possible to predict rough values for these constants. For mononuclear complexes the equation is AGf0 (M (OH),,|= AGf {M|+ By+ Cyl+ D/y, where B, C, and D are empirical parametersand y is the number of coordinated hydroxide ions. These parameters are subject to constraints that limit acceptable values. For example, B, C, and electronegativity are interrelated. This equation can be rearranged to define a new function, U, that is linearly relatedto y. This allows the interpolation of unmeasured free energies and hence formation constants. For mononuclear complexes predicted values of log Kly have an uncertainty of about±0.5. For polynuclear hydroxy complexes a relation previouslyproposed by Baes and Mesmer has been slightly modified and used to predict unknown formation constants with an uncertainty in log Kxy of about±0.5 y. Mercury (II) and silver (I), which form especially stable “linear” complexes, do not follow theabove correlations because of the structure change that occurs upon going from the M (OH) 2 to the M (OH) 3 species. The tetrahedrally coordinatedBe2+(aq) ion is more acidic than expected when compared with octahedrally coordinated aquo ions of divalent metals. Each hydrogen must carry a somewhat greater portion of the positive charge than it would in an octahedral complex, and this makes the removal of a proton easier. Aqueous Sn2+ is also unusually acidic, and it is suggested that it too has fewer water molecules in the primary coordination sphere than one would expect for a “normal” octahedrally coordinated metal ion. A reason is suggested for the experimental difficulty previous investigators have encountered in determining the formation constants for polynuclear hydroxy complexes of certain metal ions such as bismuth (III), cerium (IV), and zirconium (IV).